Production of cyanoacetic acid

ABSTRACT

Cyanoacetic acid is produced in a sequence of reactions in which an aqueous solution of chloroacetic acid neutralized with sodium carbonate or sodium hydroxide to form sodium chloroacetate which, in turn, is reacted in a nucleophilic substitution with an alkali metal cyanide and the resultant cyanoacetate is then acidified to form an aqueous reaction mixture comprising cyanoacetic acid and the respective salts formed in such reaction sequence. This process is improved A. BY CONDUCTING THE NUCLEOPHILIC SUBSTITUTION REACTION IN THE PRESENCE OF AN ALKANOL AND AT A TEMPERATURE IN EXCESS OF ABOUT 80* C. to accelerate the reaction while substantially precluding undesirable side reactions, thereby increasing the yield of the cyanoacetate and decreasing the tendency of the reaction to form color bodies; and B. BY EXTRACTING THE ACIDIFIED, AQUEOUS REACTION MIXTURE WITH AN ALKANOL WHICH CONTAINS FROM NOT LESS THAN THREE TO ABOUT 12 CARBON ATOMS AND WHICH IS SUBSTANTIALLY INSOLUBLE IN SATURATED BRINE, USING THE AQUEOUS REACTION MIXTURE IN SUCH A MANNER THAT THE AMOUNT OF SALTS IN SUCH REACTION MIXTURE SUBSTANTIALLY SATURATE THE AMOUNT OF WATER PRESENT, THEREBY PERMITTING SUBSTANTIALLY ALL OF THE CYANOACETIC ACID TO BE EXTRACTED BY THE ALKANOL. By using these improvements in a process to produce cyanoacetic acid, it is possible to obtain extremely high yields of cyanoacetic acid using much less process equipment than presently employed to produce this product. The improved process furthermore facilitates the subsequent production of alkyl cyanoacetates and of cyanoacetamide.

United States Patent Rosin et al.

[4 June 6,1972

[541 PRODUCTION OF CYANOACETIC ACID [72] Inventors: Jacob Rosin,Maplewood; Frank S. Aug,

7 Kearney, both of NJ.

[73] Assignee: Chrls CraIt Industries, Inc.-

[22] Filed: Sept. 9, 1970 [21] Appl. No.: 70,915

Related U.S. Application Data [63] Continuation-impart of Ser. No.749,940, Aug. 5,

i968, abandoned.

Primary Examiner-Joseph P. Brust AttorneyPennie, Edmonds, Morton, Taylorand Adams [5 7] ABSTRACT cyanoacetic acid is produced in a sequence ofreactions in which an aqueous solution of chloroacetic acid neutralizedwith sodium carbonate or sodium hydroxide to form sodium chloroacetatewhich, in turn, is reacted in a nucleophilic substitution with an alkalimetal cyanide and the resultant cyanoacetate is then acidified to forman aqueous reaction mixture comprising cyanoacetic acid and therespective salts formed in such reaction sequence. This process isimproved a. by conducting the nucleophilic substitution reaction in thepresence of an alkanol and at a temperature in excess of about 80 C. toaccelerate the reaction while substantially precluding undesirable sidereactions, thereby increasing the yield of the cyanoacetate anddecreasing the tendency of the reaction to form color bodies; and

- b. by extracting the acidified, aqueous reaction mixture with analkanol which contains from not less than three to about 12 carbon atomsand which is substantially insoluble in saturated brine, using theaqueous reaction mixture in such a manner that the amount of salts insuch reaction mixture substantially saturate the amount of waterpresent, thereby permitting substantially all of the cyanoacetic acid tobe extracted by the alkanol.

By using these improvements in a process to produce cyanoacetic acid, itis possible to obtain extremely high yields of cyanoacetic acid usingmuch less process equipment than presently employed to produce thisproduct. The improved process furthermore facilitates the subsequentproduction of alkyl cyanoacetates and of cyanoacetamide.

3 Claims, No Drawings PRODUCTION OF CYANOACETIC ACID Cross-Reference toRelated Application Prior Art Difficulties This application relates toan improved process for producing cyanoacetic acid and certain of itsderivatives, namely alkyl cyanoacetates and cyanoacetamide.

Cyanoacetic acid is produced in a sequence of reactions in which anaqueous solution of chloroacetic acid is neutralized with sodiumcarbonate or sodium hydroxide to form sodium chloroacetate which, inturn, is reacted in a nucleophilic substitution with an alkali metalcyanide and the resultant cyanoacetate is then acidified to form anaqueous reaction mixture comprising cyanoacetic acid and the respectivesalts formed in such reaction sequence. All of the known processes formanufacturing cyanoacetic acid have two major disadvantages. The firstof which is that the reaction between sodium cyanide and sodiumchloroacetate is very difficult to control and is accomplished by sidereactions which result in the formation of color bodies and otherimpurities as well as in the evolution of some hydrogen cyanide. Thesecond major disadvantage resides in the difficulties encountered in theisolation and work-up of cyanoacetic acid, primarily because cyanoaceticacid is extremely soluble in water. At present, most processes forproducing cyanoacetic acid require either evaporation to dryness withthe concomitant difficulties in handling such solid resides or theyemploy extractions with costly and somewhat unstable solvents, or theyemploy a combination of both techniques as described in British Pat. No.824,640. The present improvements obviate all of these difficulties.

Statement of invention Two basic improvements have been made to thereaction sequence in which an aqueous solution of chloroacetic acid isneutralized with sodium carbonate or sodium hydroxide to form sodiumchloroacetate which, in turn, is reacted in a nucleophilic substitutionwith an alkali metal cyanide and the resultant cyanoacetate is thenacidified to form an aqueous reaction mixture comprising cyanoaceticacid and the respective salts formed in such reaction sequence.

Firstly, by conducting the nucleophilic substitution reaction in thepresence of an alkanol and at a temperature in excess of about 80 C., itis possible to accelerate the reaction, thereby increasing the yield ofthe cyanoacetate and decreasing the tendency of the reaction to formcolor bodies; and

Secondly, by extracting the acidified, aqueousreaction mixture with analkanol which contains from not less than three to about 12 carbon atomsand which is substantially insoluble in saturated brine, using theaqueous reaction mixture in such a manner that the amount of salts insuch reaction mixture substantially saturate the amount of waterpresent, it is possible to permit substantially all of the cyanoaceticacid to be extracted by the alkanol, from which it may be easilyrecovered or used directly to form alkyl cyanoacetates which, in turn,may be used to produce cyanoacetamide.

Based on these discoveries, the invention contemplates the improvementin a process for the production of cyanoacetic acid, in which an aqueoussolution of chloroacetic acid is neutralized with sodium carbonate orsodium hydroxide to form sodium chloroacetate which, in turn, is reactedin a nucleophilic substitution with an alkali metal cyanide and theresultant cyanoacetate is thenacidified to form an aqueous reactionmixture comprising cyanoacetic acid and the respective salts formed insuch reaction sequence, which comprises a. conducting the nucleophilicsubstitution reaction in the presence of an alkanol and at a temperaturein excess of about 80 C. to accelerate the reaction while substantiallyprecluding undesirable side reactions, thereby increasing the yield ofthe cyanoacetate and decreasing the tendency of the reaction to formcolor bodies; and

b. extracting the acidified, aqueous reaction mixture with an alkanolwhich contain from not less than three to about l2 carbon atoms andwhich is substantially insoluble in saturated brine, using the aqueousreaction mixture in such a manner that the amount of salts in suchreaction mixture substantially saturate the amount of water present,thereby permitting substantially all of the cyanoacetic acid to beextracted by the alkanol.

Each of these process improvements may be used separately or incombination with each other. Moreover, it is possible to produce alkylcyanoacetates directly from the alkanol extract of cyanoacetic acid fromwhich alkyl cyanoacetate it is convenient to produce cyanacetamide byammoniation. Consequently, these process improvements permit theproduction of high purity cyanoacetamide in very high yields withminimum process equipment.

Basic Parameters of the Process Basically, the process for producingcyanoacetic acid in accordance with the invention comprises (1)neutralizing chloroacetic acid with sodium carbonate or sodium hydroxide(or both), (2) controlling the nucleophilic substitution reaction ofsodium chloroacetate and an alkali metal cyanide by conducting thatreaction in the presence of an alkanol, and (3) extracting the resultantcyanoacetic acid with an alkanol. The basic parameters of the processare as follows:

Neutralization of Chloroacetic Acid To avoid the formation of hydrogencyanide, the aqueous solution of Chloroacetic acid should be partiallyneutralized with sodium carbonate so that the pH is in the range from 4to 5. After such partial neutralization a vacuum (from 2080 mm. Hg.) isdrawn on the partially neutralized mixture to remove substantially allof the residual carbon dioxide from the mixture, following which theneutralization is completed with sodium hydroxide. Alternatively, sodiumhydroxide can be used exclusively as the neutralizing agent.

Control of Nucleophilic Substitution The nucleophilic substitution ofsodium chloroacetate with sodium cyanide (or potassium cyanide) must beconducted in the presence of an alkanol and at a temperature in excessof about 80 C. to accelerate this reaction while substantially avoidingor precluding undesirable side reactions. Any alkanol may be used forthis control, although best results have been obtained by usingn-butanol. Since such temperatures result in rapid completion of thenucleophilic substitution, the reaction mixture should be quenched toabout 60 C. after about 15 minutes or so, thereby protecting theend-product from degradation. Suprisingly, the use of an alkanoldecreases the tendency of the reaction to form by-products or colorbodies. Among the other alkanols which may be used are methanol,ethanol, propanol, the arnyl alcohols as well as higher alkanolscontaining up to about 12 carbon atoms.

Extraction of Cyanoacetic Acid Following the completion of thenucleophilic substitution reaction, the resultant aqueous reactionmixture is acidified to liberate cyanoacetic acid. By extracting theacidified aqueous reaction mixture with an alkanol which contains fromnot less than three to about 12 carbon atoms and which is substantiallyinsoluble in saturated brine, using the aqueous reaction mixture in sucha manner that the amount of salts in such reaction mixture substantiallysaturate the amount of water present, it is possible to permitsubstantially all of the cyanoacetic acid to be extracted by thealkanol. The most efficient alkanol for this extraction has been foundto be n-butanol. When the nucleophilic reaction between sodiumchloroacetate and the alkali metal cyanoamide is conducted in thepresence of n-butanol and when this reaction mixture is acidified withan aqueous solution of acid in an amount sufficient to liberatecyanoacetic acid from the sodium cyanoacetate, it has been found thatwhen the concentration of acid used in the acidification of the alkalimetal cyanoacetate is such that the resultant salts in the reactionmixture saturate whatever water is present, then the reaction mixturereadily separates into two phases namely 1) an alkanol phase containingsubstantially all of the cyanoacetic acid, and (2) an aqueous phase ofsaturated brine. Upon separating these two phases from each other, thecyanoacetic acid may be recovered from this reaction in yieldspreviously unobtainable.

Example A Pfaulder glass-lined reactor was charged with 1,249 lbs. ofmonochloroacetic acid and 249 gallons of water. The mixture was stirreduntil solution was achieved and 677 lbs. of sodium carbonate were addedgradually. After the sodium carbonate addition was completed, thepressure inside the reactor was lowered to about -40 mm. Hg. for about1.5-2 hours. When the reaction mixture showed a negative CO test withBa(OH) the neutralization was completed by the addition of a solutioncomprising 27.5 lbs. of NaOH in 13 gallons of water.

After the neutralization was complete, the reaction mixture wastransferred to a holding vessel from which it is continuously pumpedinto a 50 gallon reactor at a rate of 1.23 gal/min. while simultaneouslypumping into the same reactor 0.796 gal./min. ofa solution of 648 lbs.sodium cyanide in 189 gals. water and 0.681 gals/min. of n-butanol. Dueto the exothermicity of the reaction, the reaction mixture is alwaysunder reflux (temp. about 97 C.) and is 90 percent completed during the7.5 minutes residence time in the reactor. From the reactor the reactionmixture is alternately flowing into 2,250 gal. finishing vessels kept at85 C., where the reaction is completed and the reaction mixture flowsthen into a 2,000 gal. holding vessel kept at about C. From the holdingvessel the reaction mixture is continuously pumped into acidifier whilesimultaneously introducing a corresponding stoichiometric amount 25percent aq hydrochloric acid. From the acidifier the reaction mixture iscontinuously pumped into the extraction column, where it iscountercurrently extracted by n-butanol. The n-butanol extract is pumpedinto a holding vessel from which it is transferred to esterificationstill. The esterification is conducted batchwise by using toluenesolfonic acid as catalyst and removing the water azeotropically. Afterthe end of esterification, the excess n-butanol is topped off and theresidual butyl cyanoacetate is fed into the amidator as follows: To 215gals. of butyl cyanoacetate, 79 gals, methanol are added and 405 lbs.ammonia gas are introduced over a period of 4 hours, using cooling tomaintain the temperature at 23-28 C. After the end of the reaction, 79gals. n-butanol are added to the reaction mixture, methanol is toppedoff in partial vacuum and the precipitated cyanoacetamide is filteredand dried.

We claim:

1. In a process for the production of cyanoacetic acid, in which anaqueous solution of chloroacetic acid is neutralized with a neutralizingagent selected from the group consisting of sodium carbonate, sodiumhydroxide or both to form sodium chloracetate which in turn is reactedin a nucleophilic substitution with an alkali metal cyanide and theresultant cyanoacetate is then acidified to form an aqueous reactionmixture comprising cyanoacetic acid and the respective alkali metalsalts formed in such reaction sequence, the improvement which comprisesa. conducting the nucleophilic substitution reaction in the presence ofan alkanol which contains from not less than three to about 12 carbonatoms and at a temperature from about 80 C. to reflux to accelerate thereaction; and

b. extracting the acidified, aqueous reaction mixture with an alkanolwhich contains from not less than three to about 12 carbon atoms andwhich is substantially insoluble in saturated brine, using the aqueousreaction mixture in such a manner that the amount of alkali metal saltsin such reaction mixture substantially saturate the amount of waterpresent, thereby permitting substantially all of the cyanoacetic acid tobe extracted by the alkanol.

2. A process for producing cyanoacetic acid according to claim 1, inwhich (a) the nucleophilic substitution reaction is conducted in thepresence of n-butanol, and (b) the acidified, aqueous reaction mixtureof cyanoacetic acid is extracted with n-butanol.

3. A process for producing cyanoacetic acid according to claim 1, inwhich the aqueous solution of chloroacetic acid is neutralized with lessthan a stoichiometric amount of sodium carbonate achieve a pH in therange from about 4 to about 5, substantially all of the residual carbondioxide is removed from the partially neutralized mixture under vacuum,and then the neutralization is completed with sodium hydroxide beforeusing the sodium chloroacetate in the nucleophilic substitutionreaction.

2. A process for producing cyanoacetic acid according to claim 1, inwhich (a) the nucleophilic substitution reaction is conducted in thepresence of n-butanol, and (b) the acidified, aqueous reaction mixtureof cyanoacetic acid is extracted with n-butanol.
 3. A process forproducing cyanoacetic acid according to claim 1, in which the aqueoussolution of chloroacetic acid is neutralized with less than astoichiometric amount of sodium carbonate achieve a pH in the range fromabout 4 to about 5, substantially all of the residual carbon dioxide isremoved from the partially neutralized mixture under vacuum, and thenthe neutralization is completed with sodium hydroxide before using thesodium chloroacetate in the nucleophilic substitution reaction.